Hello,

I am a new bie to SLURM.  First of all, thank you for the support you are rendering to the people.

I would like to share few configuration about my cluster configuration.

1.      The hyperthreading is disabled at SLURM level in my cluster. Each of the computing node has 4 cores. Hence, no more than 4 tasks can be submitted in one computing node (they are have 4 cores).
# COMPUTE NODES
NodeName=node[1-6] Procs=4 RealMemory=15360 Sockets=1 CoresPerSocket=4 ThreadsPerCore=1 State=UNKNOWN
PartitionName=batch Nodes=node[1-6] Default=YES MaxTime=INFINITE State=UP

2.      The /proc/cpuinfo in computing nodes has the following parameters in it

CPU     0       1       2       3       4       5       6       7
apicid  16      18      20      22      17      19      21      23
core id 0       1       2       3       0       1       2       3

From these values, what I interpreted is that both the logical CPUs 0 and 4 belong to core 0, and so on.

3.      The CPU allocation during parallel tests in one computing node (each has 4 cores) is as follows

Tasks   Thread  CPUs allocated  Corresponding core id
1       1       1       1
2       1       1,4     1,0
3       1       0,1,4   0,1,0  [ core 0 is overloaded?? I Should it be something like 0,1,2 here ? ]
4       1       0,1,4,5 0,1,0,1 [ core 0 and 1 is overloaded?? Should it be 0,1,3,4?]

I use the following bash file to submit the job through slurm,

#!/bin/sh
#SBATCH --exclusive
mpirun  -x OMP_NUM_THREADS=1 -np <TASKS>  `MYAPPLICATION`  'PARAMETERS`

I see a performance drop when going beyond 2 tasks and I attribute this drop to the above reason, that is, SLURM overloading same core with more than one task. If this statement is correct, how to come out of this situation? If not, can someone tell me where things are going wrong. When I directly run with 'mpirun' command on the computing node, the tasks are spanned across  individual cores unlike the above case.

With many thanks and regards
Balachandar

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